6 A - Q [ 


OF  THE 

UNtVE.'fiSITY  of  ILLINOIS. 


rfmqtf  storage 


POTABLE  WATER 


BY 

PROFESSOR  FLOYD  DAVIS,  M.  Sc.,  Ph.  D., 

...^GJrEMtST  OF  IOWA  STATE  BOARD  OF  HEALTH. 


“ lie  who  learns  the  rules  of  wisdom  without  conforming  to  them  in  his  lifey 
is  like  a man  who  labored  in  his  fields  but  did  not  sow — Saadi. 


L!  cn  Aii.i 

OF  THE 

UNIVERSITY  of  ILLINOIS. 


POTABLE  WATER. 

« 

I.  PURE  WATER. 

Water  is  a chemical  compound  of  hydrogen  and  oxygen,  which 
is  widely  diffused  in  nature.  As  a solid,  it  exists  as  snow  and  ice; 
as  a liquid,  it  constitutes  streams,  lakes  and  seas,  and  in  a state  of 
minute  subdivision,  mist  and  clouds;  while  as  a colorless  gas,  it  is 
always  a constituent  of  the  air.  Natural  waters  are  always  impreg- 
nated with  certain  foreign  constituents  which  give  to  them  their 
varying  properties;  and  in  the  examination  of  water  for  sanitary 
purposes,  it  is  not  the  water  which  is  analyzed,  but  its  impurities. 

The  palatability  of  water  depends  upon  its  occluded  gases,  which 
are  principally  oxygen,  nitrogen,  carbonic  anhydride  and  hydrogen 
sulphide.  These  gases  are  readily  absorbed,  and  they  give  to  the 
water  an  agreeable  taste,  and  a sparkling  brilliancy.  The  high 
degree  of  palatability  of  spring-water  is  mainly  due  to  its  carbonic 
anhydride.  Distilled  water,  or  water  deprived  of  its  gases  by  boil- 
ing, is  insipid  or  u flat ; ” but  by  aeration  and  acidification  it  regains 
its  palatability.  Water  must  be  more  or  less  impregnated  with 
gases  before  it  is  even  suitable  to  the  dietetic  needs  of  man;  for 
when  water  deprived  of  its  gases,  is  used  for  purposes  of  experi- 
ment, it  is  found  to  be  prejudicial  to  health,  as  the  stomach  cannot 
gratefully  receive  and  advantageously  appropriate  it.  (*) 

Researches  in  etiology  have  shown  that  the  health  of  an  individ- 
ual, or  of  a community,  depends  largely  upon  the  purity  of  the 
water  supply.  It  is  not  chemically  pure  water,  however,  that  is 
needed  for  the  maintenance  of  perfect  health,  for  such  water  does 
not  exist  in  nature.  As  chemically  pure  water  contains  nothing 
injurious  to  the  system,  it  likewise  contains  nothing  beneficial,  and 
for  healthy  persons,  such  water  is  not  the  most  wholesome.  The 

(!)  Van  Nostrand’s  Engineering  Magazine,  December,  1872,  p.  593. 


— 4— 


healthy  human  system  ordinarily  requires  mild  cathartics  and  other 
mineral  salts  for  the  continuity  of  health.  These,  in  part,  can  be  best 
furnished  to  the  system  as  the  mineral  constituents  of  potable  water. 
The  wholesomeness  of  water  is  therefore  increased  by  the  presence  of 
small  quantities  of  certain  mineral  salts,  in  solution,  which  act  as  laxa- 
tives, and  which  are  essential  to  the  development  of  animal  tissue; 
but  drinking  water  should  be  free  from  organic  impurities.  As  a 
rule,  chemists  condemn  all  waters  which  are  contaminated  with  sew- 
age, such  contamination  being  shown  by  chemical  and  micro- 
scopical analyses,  and  by  an  examination  of  the  sources  of  supply. 
From  a sanitary  standpoint,  pure  water  may  be  defined  as  water 
which  is  unobjectionable  for  general  domestic  use,  and  especially  that 
which  may  be  used  with  perfect  safety  for  drinking  purposes. 

Some  waters  are  so  unpotable  that  the  appetite  does  not  demand 
the  amount  required  for  the  normal  functions  of  the  body.  Such 
waters  not  only  lessen  bodily  vigor  and  frequently  produce  disease, 
but  an  insufficient  supply  of  any  water  is  manifested  by  great  pain,  re- 
laxation of  muscular  strength  and  of  mental  vigor,  and  diminution  in 
the  elimination  of  pulmonary  carbonic  anhydride  and  bodily  excre- 
tions. So,  when  we  consider  that  about  seventy (2)  per  cent  of  the 
human  body  is  composed  of  water,  which  is  being  constantly 
eliminated,  the  need  of  maintaining  a copious  supply  of  pure  water 
becomes  apparent;  but  an  abundance  of  water  is  no  more  necessary 
to  the  support  of  life  than  its  purity  is  to  the  continuity  of  health. 
People  may  habitually  drink  impure  water  and  still  live,  but  its 
use  unquestionably  affects  the  human  system  and  tends  to  the  degen- 
eration of  a race.  Experience  shows  that  even  slightly  impure 
water  may  be  productive  of  a host  of  ailments  for  which  the  sufferer 
finds  no  apparent  cause;  for  the  results  are  often  so  slow  and  grad- 
ual as  to  evade  ordinary  observation,  and  the  evil  is  borne  with 
the  indifference  and  apathy  of  custom.  It  is  only  when  striking 
and  violent  effects  are  produced  that  public  attention  is  arrested. 

A water  which  is  constantly  used  for  domestic  purposes  should 
have  the  following  qualities: 


(2)  Human  Physiology,  Dalton,  Seventh  Edition,  p.  36. 


— 5— 


1.  It  should  be  free  from  odor  and  taste. 

2.  It  should  be  free  from  dead  vegetable  and  animal  organ- 
isms, and  should  contain  only  such  living  forms  as  are  purifying 
agents. 

3.  It  should  at  all  seasons  of  the  year  be  well  aerated,  uniform 
in  temperature,  and  free  from  suspended  matter. 

4.  It  should  contain  only  a small  quantity  of  mineral  matter 
in  solution,  and  be  free  from  all  the  poisonous  salts. 

For  persons  afflicted  with  renal  diseases,  distilled  water  in  its 
crystalline  purity  is  probably  the  most  healthy  beverage,  for  it  acts 
upon  the  kidneys  as  a powerful  therapeutic  agent  in  the  solution 
and  removal  of  the  waste  products  of  the  body.  Upon  this  point 
Professor  Charles  Mayr(3)  says : 4 ‘ Those  who  have  never  drunk  pure 

water  do  not  realize  what  an  effect  such  water  has  upon  the  kidneys; 
its  effect  is  better  than  that  of  acetates,  nitrates,  opiates  or  alcohol, 
and  for  people  with  tendency  to  kidney  diseases  or  Dropsy  there  is 
no  better  drug  than  pure  water.  Of  the  thousands  of  chemical 
compounds  and  waste  products  found  in  the  human  system,  many 
require  pure  water  for  their  solution  and  elimination;  and  water  so 
overloaded  with  salts  as  average  well-water  will  not  work  satis- 
factorily.” 


II.  INORGANIC  IMPUEITIES. 

Water  is  the  most  nearly  universal  solvent  in  nature,  and  as  it 
passes  into  the  earth,  charged  with  atmospheric  gases,  it  dissolves 
many  salts.  When  it  reappears  again  on  the  surface  in  springs, 
and  flows  away  in  streams,  it  is  often  heavy  laden  with  mineral  con- 
stituents; but  the  streams  and  lakes  in  granite  regions  are  very 
nearly  pure.  The  oceans  and  inland  seas  are  the  final  reservoirs  of 
flowing  water,  and  they  become  saline  from  the  concentration  of 
their  mineral  matter,  through  evaporation.  Sea  water  contains 
about  two  thousand  grains  of  total  solids  per  gallon,  while  the 
waters  of  the  Great  Salt  Lake  and  the  Dead  Sea  each  contain  about 
twelve  thousand  grains.  (4) 


(3)  Report  of  New  Jersey  State  Board  of  Health,  1887,  p.  338. 
<4)  Manual  of  Mineralogy  and  Petrography,  Dana,  p.  252. 


—6— 


From  an  examination  of  the  water  supplies  of  sixty-five  Eng- 
lish and  Scotch  cities  and  towns,  Dr.  H.  Letherby,(5)  an  emi- 
nent English  chemist  and  sanitarian,  concluded  that  the  rate  of 
mortality  was  inversely  as  the  amount  of  mineral  salts  in  the  water 
supplies. 

Only  certain  constituents,  however,  are  beneficial  to  health;  others 
are  deleterious;  and  a water  which  contains  too  large  an  amount  of 
mineral  salts  should  be  avoided,  as  it  is  liable  to  produce  derange- 
ments in  the  alimentary  canal. 

When  the  amount  of  mineral  constituents  in  water  becomes  so 
excessive  as  to  give  it  decided  medicinal  properties,  the  water  is 
styled  mineral  or  abnormal.  Many  salts  have  a characteristic  taste, 
and  the  nature  of  mineral  waters  can,  therefore,  often  be  determined 
by  the  sense  of  taste  alone.  Mineral  waters  are  classified  according 
to  the  principal  substance  in  solution.  Thus  a chalybeate  water 
has  in  solution  an  excess  of  an  iron  salt,  usually  carbonate  or  sul- 
phate, and  which,  upon  standing  exposed  to  the  air,  generally 
deposits  a yellow  precipitate  of  carbonate  of  iron;  a saline  water 
has  in  solution  an  excess  of  some  salt,  like  sodium  chloride,  or 
sodium  and  magnesium  sulphate;  a carbonated,  effervescent  or 
acidulous  water  has  carbonic  anhydride  in  excess;  while  a sulphur 
or  hepatic  water  contains  an  excess  of  hydrogen  sulphide.  Upon 
standing,  hepatic  waters  become  somewhat  turbid  and  deposit  sul- 
phur. 

Saline  waters,  when  used  occasionally  and  moderately,  are  bene- 
ficial to  health,  owing,  in  part,  to  the  cathartic  action  of  the 
sulphates  and  phosphates  of  the  alkalies  and  alkaline-earths,  which 
are  usually  found  in  such  waters;  but  their  excessive  use,  or  the 
prolonged  use  of  waters  containing  too  much  salts  in  solution, 
should  be  avoided.  Saline  waters  often  afford  relief  to  persons 
afflicted  with  Inflammatory  Rheumatism,  when  they  are  frequently 
used  for  bathing  purposes.  Carbonated  waters  are  not  only  highly 
palatable,  but  they  are  very  beneficial  to  persons  suffering  from 
Dyspepsia.  But  waters  containing  much  hydrogen  sulphide  are 


(6)  Report  of  Michigan  State  Board  of  Health,  1876,  p.  78. 


—7— 


not  really  wholesome,  as  they  will  produce  Diarrhea,  (6)  especially 
if  organic  matter  be  present;  but  in  small  quantity  hydrogen 
suphide  is  not  in  any  way  injurious  to  health. 

Some  salts  are  productive  of  Indigestion,  and  in  many  cases  Con- 
stipation and  visceral  obstruction  are  induced  by  the  use  of  mineral 
waters.  Chalybeate  waters  not  unfrequently  induce  in  the 
drinker,  Headache,  Indigestion  and  Dyspepsia.  A drinking  water 
should  not  contain  more  than  one  fifth(7)  of  a grain  of  iron  per 
gallon.  Calcium  and  magnesium  chlorides  and  sulphates  will  pro- 
duce Chronic  Diarrhea,  and  if  the  water  also  contains  ammonium 
and  calcium  nitrates  and  sodium  chloride  in  excess,  and  is  used 
freely,  it  is  sometimes  the  cause  of  Dysentery.  Dyspepsia  is  also 
frequently  produced  by  water  containing  calcium  and  magnesium 
salts.  Goitre,  so  frequently  found  among  the  inhabitants  of  some 
of  the  valleys  of  Switzerland,  is  caused  by  the  excessive  permanent 
hardening  constituents  of  the  water.  A water  containing  not  more 
than  seven(8)  grains  of  salts  per  gallon  is  said  to  be  injurious  to 
many  persons.  uWith  regard  to  the  total  quantity  of  impurities 
admissible  in  good  drinking  water,  the  Sanitary  Congress  which 
met  at  Brussels  decided  that  water  containing  more  than  thirty-five 
grains  of  impurity  in  one  gallon  is  not  wholesome,  and  that  there 
should  not  be  much  more  than  one  grain  of  organic  matter.”(9) 

The  normal  carbonates  of  the  alkaline-earths,  magnesium  and 
iron,  are  practically  insoluble  in  pure  water.  (10)  But  the  bicarbon- 
ates of  these  metals,  which  are  readily  soluble,  are  formed  by  the 
union  of  carbonic  anhydride  and  water,  with  the  normal  carbonates, 
and  there  is  scarcely  a natural  water  which  does  not  contain  a small 
amount  of  them.  It  is  claimed  by  some  eminent  authorities  that 
small  quantities  of  these  bicarbonates  in  drinking  water  are  bene- 
ficial to  health;  but  experience  has  also  shown  that  large  quantities 

(6)  Practical  Hygiene,  Parkes,  Seventh  Edition,  p.  58. 

(7)  Water  Analysis,  Wanklyn  and  Chapman,  Sixth  Edition,  p.  61. 

(8)  Practical  Hygiene,  Parkes,  Seventh  Edition,  p.  56. 

(9)  Report  of  American  Public  Health  Association,  Vol.  I,  p.  538. 

(10)  “ About  one  grain  of  calcium  carbonate  to  the  gallon  is  usually  stated  to  be  the 
proportion  dissolved,  but  it  has  been  pointed  out  lately  by  Allen,  that  this  is  an  under- 
statement, since  solutions  have  been  obtained  containing  twice  this  amount.”— 
[Examination  of  Water  for  Sanitary  and  Technical  Purposes,  Leffmann  and  Beam,  p. 


— 8— 


of  these  salts  are  sometimes  injurious.  If  in  excess,  they  are 
decomposed  in  passing  through  the  system,  and  give  rise  to  renal 
and  bladder  difficulties,  which  often  culminate  in  Gravel.  The 
bicarbonates  are  not  generally  found  in  well-waters  in  excessive  or 
dangerous  quantities;  but  the  continued  use  of  spring-water  which 
flows  from  limestone  rock  will  eventually  give  rise  to  disease,  for 
communities  which  use  only  limestone  water  are  generally  afflicted 
with  diseases  which  arise  from  overworked  kidneys.  These  bicar- 
bonates are  the  constituents  of  temporary  hardness  in  water,  and 
they  can  be  removed  by  boiling,  as  by  this  operation  bicarbonates 
are  decomposed  into  normal  carbonates,  which  precipitate,  and 
carbonic  anhydride  and  water  which  escape.  Water  is  usually 
rendered  permanently  “hard”  by  the  solution  of  the  sulphates  of 
calcium,  magnesium  and  iron. 

The  salts  of  some  elements,  like  arsenic,  antimony,  barium, 
chromium,  zinc,  copper  and  lead,  are  dangerous  poisons,  and 
water  containing  even  traces  of  them  should  always  be  avoided. 
Lead  poisoning  is  not  unfrequent  in  some  cities  where  the  water 
for  domestic  use  passes  through  lead  pipes.  Aerated  water  tends 
to  dissolve  lead,  forming  a hydrate,  which  in  presence  of  carbonic 
anhydride  in  excess,  forms  a slightly  soluble  bicarbonate  of  lead. 
Chlorides  and  nitrates  in  water  also  tend  to  form  insoluble  com- 
pounds on  the  inner  surface  of  the  pipes,  which  prevent  further 
action  of  the  oxygen  upon  the  lead.  Lead  pipes  should,  therefore, 
only  be  used  in  conveying  drinking  water,  which  contains  an  excess 
of  sulphates  or  normal  carbonates  in  solution.  Indeed,  it  is 
doubtful  whether  lead  pipes  should  be  used  at  all  for  a water  sup- 
ply, as  a water  which  contains  a sufficient  quantity  of  the  necessary 
salts  to  prevent  the  solution  of  lead,  is  liable  to  produce  derange- 
ments in  the  alimentary  canal. 

Potable  water  often  contains  suspended  mineral  matter,  such  as 
sand  and  clay,  and  it  is  believed  that  an  excessive  turbidity  caused 
by  these,  is  productive  of  intestinal  difficulties,  Indigestion, 
Dyspepsia  and  Diarrhea.  The  character  of  the  suspended  matter 
can  only  be  fully  determined  by  means  of  the  microscope. 


—9— 


III.  VEGETABLE  IMPURITIES. 

r 

The  turbidity  of  water  is  sometimes  produced  by  decomposing 
organic  matter,  which  is,  with  the  exception  of  pathogenic  germs, 
the  most  deleterious  of  all  impurities. 

Although  the  products  of  vegetable  decay  indirectly  produce 
malarious  diseases,  they  are  not  in  themselves  especially  injurious 
to  the  human  system ; they  merely  furnish  a pabulum  in  which  cer- 
tain disease  germs  flourish,  for  the  malarious  influence  is  attributed 
by  medical  science  to  micro-organisms.  These  living  germs  are 
most  frequently  conveyed  to  the  system  in  the  air,  but  the  most 
dangerous  types  of  malaria  are  caused  by  polluted  water,  which 
seems  to  be  a more  concentrated  and  dangerous  poison  than  malari- 
ous air.  And  in  the  production  of  remittent  fever (u)  by  malarious 
surface-water,  it  is  noticeable  that  the  disease  is  always  of  a more 
aggravated  type  than  when  caused  by  exhalations  from  miasmatic 
soil.  So,  water  which  shows  by  analysis  that  it  contains  decom- 
posing vegetable  matter,  should  always  be  avoided. 

By  the  drainage  of  swamps  and  the  cultivation  of  the  soil,  com- 
munities have  often  freed  themselves  of  much  sickness  of  a dangerous, 
malarious  character.  Decaying  wood,  like  pump-stocks  and  storage- 
tanks,  often  produce  harmful  results,  through  the  water,  and  the 
decomposition  of  sawdust  (12)  in  water  is  a fruitful  source  of  all 
forms  of  malarious  fever. 

Many  cases  are  on  record  from  the  American  Civil  War,  in  which 
the  use  of  surface-water,  impregnated  with  the  debris  of  plants, 
like  cellular  tissue  and  chlorophyl,  also  produced  Diarrhea ; but 
when  such  water  was  filtered  the  disease  abated.  (13)  The  water 
supplies  of  some  of  the  eastern  cities  have  at  times  a decidedly  fish- 
like odor,  which  Professor  Lattimore  has  shown  to  be  due  to  the 
presence  of  Algos, , perhaps  in  a state  of  decomposition.  The  little 
filaments  of  decomposing  Algos,  when  seen  under  the  microscope, 
are  usually  changed  in  color  and  broken  down  in  structure.  It  is 


(U)  Water  Supply  of  U.  S.  Capitol,  49th  Congress,  1st  Session,  Ex.  Doc.  No.  154,  pp.  8-9. 
(12J  Report  of  Michigan  State  Board  of  Health,  1882,  p.  155. 

(13)  Practical  Hygiene,  Parkes,  Seventh  Edition,  p.  57. 


10— 


the  opinion  of  the  most  competent  judges  that  waters  containing 
such  filaments,  if  used  for  a considerable  length  of  time,  are  very 
injurious  to  health ; and  certain  Algoe  in  a water  supply  are  some- 
times accompanied  by  an  alarming  mortality  of  fish.(14)  Pond 
water,  in  which  there  is  a copious  growth  of  aquatic  plants,  is  said 
to  produce  intestinal  worms. 

Recent  investigations^5)  have  shown  that  many  varieties  of  Algae 
are  probably  capable  of  producing  an  objectionable  taste  and  odor 
in  water,  which,  in  case  of  the  grass-green  varieties,  are  especially 
rancid ; but  power  to  produce  these  changes  is  entirely  independent 
of  color.  Nostoc , a greenish,  gelatinous,  translucent  variety  of 
Algae , which  develops  rapidly  in  wet  places  after  a rain,  is  a fre- 
quent source  of  contamination  of  water ; and  it  is  of  especial  inter- 
est in  this  connection  as  being  the  chief  source  of  the  unpleasant 
u pig-pen”  odor  of  water.  The* intensity  of  the  physical  exponents, 
taste  and  odor,  may  be  taken  as  a measure  of  the  rapidity  of  decom- 
position of  the  Algae  present  in  water  at  any  given  time,  and  they 
are  consequently  a measure  of  its  cryptogamic  pollution. 

But  there  are  certain  living  Algae  that  may  be  taken  as  a measure 
of  the  organic  pollution  of  water.  Thus,  the  Flagillata  are  gener- 
ally found  in  water  containing  decaying  infusions  of  vegetable  and 
animal  matter,  and  they  have  been  detected  in  the  dejections  from 
Cholera  and  Typhoid  Fever  patients.  The  Beggiatoa  alba , a species, 
of  Algae  closely  resembling  some  forms  of  Bacteria , is  also  only 
found  in  stagnant  waters,  and  it  is,  therefore,  indicative  of  harmful 
pollution. 

Some  waters  which  come  from  clay  soil  have  so  strong  an  odor  of 
hydrogen  sulphide  and  sulphuretted  hydro-carbons  as  to  be  undrink- 
able, and  yet  the  organic  matter  in  them  will  not  often  warrant  their 
condemnation.  These  gases  are  probably  produced  in  the  decom- 
position and  reduction  of  sulphates,  by  decomposing  organic  matter, 
and  by  living  Bacteria  and  low  forms  of  Algae.  According  to 
Professor  Nichols,  (16)  decaying  organic  matter,  in  water,  under 

(i±)  On  the  Micro-Organisms  in  Hemlock  Water,  Rafter,  p.  16. 

(15)  On  the  Fresh  Water  Algae,  and  Their  Relation  to  the  Parity  of  Public  Water  Sup- 
plies, Rafter,  p.  2. 

(16)  On  the  Fresh  Water  Algae,  and  Their  Relation  to  the  Purity  of  Public  Water  Sup- 
plies, Rafter,  p.  10. 


—11— 


favorable  conditions  of  temperature,  reduces  sulphates  to  sul- 
phides, and  from  these,  hydrogen  sulphide  is  liberated  by  the  acid 
products  of  decay. 

The  genus  Beggicttoa  only  exist  in  water  containing  some  form  of 
sulphur,  when  free  from  iron.  (17)  These  organisms  probably  possess 
the  power  of  extracting  sulphur  from  decomposing  organic  matter 
containing  it,  with  the  liberation  of  hydrogen  sulphide.  They  also 
possess  the  power  of  extracting  sulphur  from  sulphates  in  water, 
appropriating  the  sulphur  in  an  amorphous  state  into  the  proto- 
plasmic mass  of  their  cell  structure,  with  the  liberation  of  the  balance 
of  the  sulphur  as  hydrogen  sulphide.  The  presence  of  hydrogen 
sulphide  in  a water  supply  is,  therefore,  no  reliable  indication  of 
organic  pollution. 

Pure  water  in  thin  layers  is  almost  colorless,  but  in  considerable 
volume  it  has  a decidedly  bluish  tint,  which  comes  from  its  power 
to  absorb,  reflect,  and  transmit  white  light.  Rain-water  is  some 
times  highly  colored  with  vegetable  matter  from  the  roofs  of  build- 
ings, but  it  is  often  the  healthiest  of  drinking  water,  on  account  of 
the  stability  of  its  organic  matter.  The  chlorophyl  of  unicellular 
Algae , growing  in  water,  often  colors  the  water  green.  Peat  gives 
to  water  a brownish  color,  but  analyses  and  long  continued  use 
demonstrate  that  such  water  is  usually  wholesome.  It  is  true  that 
such  water  has  sometimes  a laxative  effect  upon  the  system,  but  its 
action  is  only  temporary,  and  so  can  in  no  sense  be  injurious.  Peat 
water  is  often  used  for  drinking  purposes  on  long  ocean  voyages, 
on  account  of  its  power  of  retaining  freshness. 

IV.  ANIMAL  IMPURITIES. 

The  products  of  decomposition  of  animal  matter  are  always  more 
dangerous  to  the  human  system  than  those  from  vegetation,  as  some 
of  them  are  highly  nitrogenous;  and  water  which  is  contaminated 
with  the  animal  accumulations  of  sewers,  cess-pools,  and  privies,  is 
a most  loathsome  and  dangerous  poison.  A microscopic  examina- 
tion of  polluted  water  often  reveals  the  presence  of  hair,  excreta, 
intestinal  epithelial  cells,  and  living  organisms.  Such  water  should 


(17)  Water  Analysis,  McDonald,  p.  25. 


—12— 


be  absolutely  condemned  for  all  sanitary  purposes,  as  the  impuri- 
ties could  only  come  from  sewers  and  privy-vaults,  and  the  living 
organisms  feast  upon  the  products  of  decay. 

Animal  matter  is  highly  putrescible,  and  water  containing  it  is 
liable  to  produce  putrefactive  changes  in  persons  drinking  it.  The 
nitrogenous  matter  decomposes  by  oxidation  and  disintegration, 
through  the  agency  of  micro-organisms,  producing  in  its  earlier 
stages,  Ptomaines , bodies  which  are  closely  allied  to  the  vegetable 
alkaloids,  but  more  susceptible  of  decomposition.  Although  the 
Ptomaines  are  present  in  very  small  quantity  in  polluted  water, 
yet  they  are  very  active  in  their  physiological  effects,  and  produce 
harmful  results  when  taken  into  the  system.  Other  products  of 
decomposition  furnish  a suitable  pabulum  for  the  accumulation  and 
multiplication  of  germs  of  disease.  Many  contagious  and  infec- 
tious zymotic  diseases  are  produced  by  water  polluted  with  decom- 
posing animal  matter,  and  indeed,  it  is  highly  probable  that  certain 
diseases  are  seldom  produced  in  any  other  way.  (18)  Polluted  waters 
are  often  deceptive,  since  they  generally  have  an  agreeable  taste 
and  are  highly  palatable. 

In  the  Fall  of  1887,  Typhoid  Fever  became  epidemic  in  Ottawa, 
Minneapolis,  Pittsburgh,  and  many  other  cities,  and  it  was  found 
on  examination  that  in  every  case  known  to  the  writer,  the  disease 
was  communicated  through  potable  water.  In  Pittsburgh  the  cir- 
cumstances were  especially  interesting.  The  south  side  of  the  city 
was  supplied  by  the  Monongahela  Water  Co.’s  works,  and  the  fever 
was  located  in  districts  supplied  by  that  company.  Upon  chemical 
and  microscopical  examination  of  the  water,  the  pollution  was 
traced  many  miles  above  the  city  to  a ravine  into  which  drained  the 
privies  of  houses  where  four  Typhoid  Fever  patients  had  been  loca- 
ted several  weeks  before.  (19) 

From  1856  to  1866  there  were  twenty-one  thousand  deaths  from 

(18)  “ There  is  abundant  proof  that  drinking  water  has  been  instrumental  in  the 
spread  of  the  following  diseases:  Cholera,  Typhoid  Fever,  Dysentery,  Diarrhea 
Diphtheria,  Malaria,  Cholera  Infantum,  and  Cerebro-spinal  Meningitis;  and  in  addition 
to  these,  certain  low  forms  of  fever  to  which  no  other  name  than  Continued  Fever  can 
be  given.”— [Report  of  Brooklyn  Commissioner  of  Health,  March  10, 1884,  p.  19,] 

(19;  Report  of  Special  Committee  on  South  Side  Water  Supply,  Pittsburgh,  Decem- 
ber 23d,  1887.  • 


LIBRARY 

OF  THE 

UNIVERSITY  of  ILLINOIS. 

-13- 

Cholera,  and  one  hundred  and  fifty  thousand  deaths  from  Typhoid 
Fever,  in  England  and  Wales  ;(so)  while  now  in  all  of  Great  Britain 
twenty  thousand  persons  die  and  two  hundred  thousand  suffer  annu- 
ally from  Typhoid  Fever,  and  the  majority  of  cases  are  produced  by 
polluted  water.  (21) 

In  Michigan  the  annual  mortality  from  Typhoid  Fever  is  about 
one  thousand,  while  ten  thousand  persons  are  annually  afflicted 
with  this  disease.  (22) 

In  the  United  States  thirty  thousand  people  die  annually  from 
this  fever  alone.  The  mortality  from  Typhoid  Fever  in  many  of 
the  eastern  cities  is  proportional  to  the  quantity  of  sewage  which 
enters  the  water  supplies.  (23)  The  annual  death  rate  from  this 
disease  per  one  hundred  thousand  inhabitants  in  Brooklyn  is 
about  fifteen,  in  Hew  York  city  twenty-five,  and  in  Boston  forty  ; 
while  in  the  city  of  Vienna,  from  1851  to  1874,  while  impure 
well-water  and  a supply  from  the  Danube  were  used,  the  annual 
death-rate  was  from  one  hundred  to  three  hundred  and  forty  per 
one  hundred  thousand  inhabitants.  By  the  use  of  spring-water  in 
place  of  the  former  supplies,  the  mortality  from  Typhoid  Fever,, 
in  Vienna,  has  been  greatly  reduced.  During  the  last  three  years 
the  annual  death-rate  in  that  city  has  only  reached  eleven  per  one 
hundred  thousand  inhabitants. 

Some  of  the  lowly-organized  animal  scavengers,  which  assimilate 
the  decomposition  products  of  organic  matter,  are  injurious  to  the 
human  system,  but  the  majority  of  them  are  harmless,  and  nearly 
all  of  them  are  purifying  agents. 

Polluted  water  is  generally  infested  with  Infusoria.  (24)  This  is 
especially  true  of  stagnant  surface-water,  and  the  water  from  many 
surface  wells.  Recent  investigations  in  biology  demonstrate  that 
nitrogenous  food  is  necessary  for  the  development  of  such  life  in 
water  ; but  there  are  certain  conditions  not  yet  clearly  understood, 

(20)  Report  of  Brooklyn  Commissioner  of  Health,  March  10, 1884,  p.  78. 

(21)  Report  of  Michigan  State  Board  of  Health,  1884,  p.  116. 

(22)  Report  of  Michigan  Sanitary  Convention,  December  6 and  7, 1887,  p.  24. 

(23)  Report  of  Committee  on  the  Pollution  of  Water  Supplies,  American  Public 
Health  Association,  1888,  p.  5. 

(24)  “The  Animal  World  of  Well-waters,”  Popular  Science  Monthly,  June,  1889,  pp. 
251-257. 


—14— 


favoring  the  transformation  of  harmless  organic  matter,  in  presence 
of  nitrogen  salts  and  phosphates,  into  a favorable  pabulum  for  the 
growth  of  micro-organisms.  (25)  Phosphates  are  not  usually  found 
in  potable  water,  and  the  presence  of  infusorial  life  in  water  free 
from  phosphates,  is,  therefore,  very  reliable  evidence  of  its  pollu- 
tion. 

The  ciliated  embryos  of  certain  Entozoa  are  sometimes  found  in 
potable  water.  They  are  generally  very  active  in  early  life,  but 
finally  lose  their  ciliated  covering  and  perish,  unless  they  find  their 
way  into  the  body  of  some  animal  drinking  the  water. 

Cyclops , or  water  flea,  is  one  of  the  most  common  genera  of 
Entomonstraca  found  in  potable  water.  Dr.  H.  C.  Sorby(26)  has 
shown  that  the  number  of  certain  of  the  Entomostraca  in  water 
may  be  taken  as  a measure  of  its  organic  pollution,  for  an  increase 
in  sewage  is  indicated  by  an  increase  in  their  total  number,  or  by 
an  alteration  in  the  relative  number  of  each  species,  or  by  both. 
It  is  not  known  whether  Infusoria , Entomostraca , and  certain  forms 
of  microscopical  animal  life  are  the  agents  or  the  companions  of 
disease,  but  serious  outbreaks  of  Fever,  Diarrhea,  and  Dysentery 
have  been  produced  by  water  swarming  with  these  forms  of  life.  (27) 

Leeches  are  sometimes  accidentally  swallowed  in  potable  water. 
They  are  liable  to  attach  themselves  on  the  pharynx,  and  when 
once  fixed  they  seldom  fall  off  spontaneously.  Coughing,  nausea, 
and  spitting  of  blood  are  produced  by  them,  and  repeated  bleeding 
from  the  larynx  produces  anaemia.  (28) 

Y.  BACTERIA  IN  WATER. 

Living  germs  are  even  more  dangerous  in  drinking  water  than 
animal  organisms  and  dead  organic  matter.  Some  diseases,  such 
as  Cholera,  Typhoid  Fever  and  Diphtheria,  are  generally  believed 
to  be  produced  by  micro-organisms,  which,  like  the  spores  of  some 
plants,  are  thrown  off  with  the  excretions  of  persons  suffering  with 

(25)  On  The  Micro-Organisms  in  Hemlock  Water,  Rafter,  p.  4. 

(26)  On  the  Micro-Organisms  in  Hemlock  Water,  Rafter,  p.  25. 

(27)  On  the  Use  of  the  Microscope  in  Determining  the  Sanitary  Value  of  Potable 
Water,  Rafter,  p.  11. 

(28)  Practical  Hygiene,  Parkes,  Seventh  Edition,  p.  78. 


—15— 


the  disease,  and  they  find  their  way  mainly  through  the  water  sup- 
ply, to  those  who,  from  predisposing  causes,  are  in  a suitable  con- 
dition for  the  reception  and  multiplication  of  the  germs  and  the 
production  of  the  specific  form  of  disease.  These  pathogenic  micro- 
organisms are  known  as  Bacteria , and  the  diseases  which  they  pro- 
duce, zymotic,  in  consequence  of  their  course  resembling  a process 
of  fermentation;  but  only  few  Bacteria  are  pathogenic.  The  most 
common  forms  of  these  organisms  are  not  more  than  one  fifteen 
thousandth  or  one  twenty  thousandth  of  an  inch  in  length,  and  it 
has  been  estimated  that  it  would  require  four  hundred  million  of 
them  of  average  size,  to  cover  one  square  inch  of  surface.  In  their 
multiplication,  a single  germ  becomes  the  causative  parent  of  thirty 
or  forty  million  descendents  in  a day. 

In  an  interesting  investigation (29)  at  the  city  of  Paris  it  was 
found  that  in  a cubic  metre  of  air  above  ground  there  were  ten 
thousand  germs;  in  the  sewers,  thirty-six  thousand;  in  old  houses, 
forty  thousand;  and  in  the  hospital  of  Petie,  seventy  thousand. 
And  these  organisms  are  absorbed  by  water  exposed  to  the  air. 

Dr.  Percy  F.  Frankland(30)  has  found  that  average  river-water, 
like  the  Thames,  contains  about  twenty  thousand  germs  per  cubic 
centimetre,  and  that  this  number  is  greatly  reduced  when  the  water 
is  submitted  to  storage  and  filtration;  but  there  is  no  reliable  artifi- 
cial method  for  their  entire  removal,  except  by  the  agency  of  heat. 

Bacteria  are  almost  universal  in  all  kinds  of  matter.  They  in- 
habit the  air  we  breathe  and  the  food  we  eat,  and  even  the  purest 
water  is  never  free  from  them.  The  harmless  forms  of  Bacteria 
have  their  uses  in  the  economy  of  nature.  It  is  to  them  that  we 
owe  the  phenomena  of  fermentation  and  decay,  as  they  effect  a 
transmutation  in  organic  substances,  and  finally  elaborate  them 
nto  organic  products.  By  the  united  efforts  of  Bacteria , sugar 
is  converted  into  alcohol,  and  the  cork  of  the  champagne  bottle  is 
discharged  with  explosive  violence.  While  one  class  of  Bacteria  is 
thus  engaged  in  making  alcohol,  another  class  is  fermenting  it  into 


(29)  Water,  Moore,  p.  7. 

(39)  Report  of  Maine  State  Board  of  Health,  1887,  p.  316. 


—16 


acetic  acid;  and  other  classes  still  are  servants  to  the  baker  in  rais- 
ing his  bread. 

Each  group  of  pathogenic  Bacteria  has  its  specific  organ  for  at- 
tack. Thus  the  Bacillus  Tuberculosis  generally  has  its  seat  in  the 
lungs;  the  Typhoid  Bacillus  penetrates  the  mucus  membranes  of  the 
intestines  and  accumulates  in  the  spleen;  and  the  Bacillus  of  Diph- 
theria produces  extensive  layers  of  false  membranes  in  the  fauces. 
Each  group  has  its  own  distinctive  character;  some  seem  to  evolve 
higher  types  of  life;  some  prey  upon  and  seem  to  devour  others; 
and  they  are  quite  probably  the  cause  or  the  result  of  every  zymotic 
disease. 

In  some  instances,  Bacteria  are  capable  of  being  conveyed  to 
great  distances  in  water,  without  losing  the  vitality  necessary  to 
produce  disease.  Indeed,  it  is  a very  difficult  matter  to  deprive 
some  forms  of  Bacteria  of  their  vitality;  they  may  be  frozen  or 
even  heated  to  the  boiling  point  of  water  and  yet  many  of  them 
are  not  destroyed.  They  may  be  kept  dried  for  years,  and  when 
placed  in  a favorable  medium  are  yet  capable  of  producing  disease. 

The  noted  outbreak  of  Typhoid  Fever  at  Lausen,  Switzerland, 
and  at  Plymouth,  Pennsylvania,  has  shown  that  the  dejections  from 
a single  Typhoid  Fever  patient  are  sufficient  to  poison  the  water 
supply  of  a whole  town,  and  give  rise  to  an  extended  outbreak  of 
fever.  It  is,  therefore,  apparent  that  human  faecal  matter  is  very 
dangerous,  as  it  may  contain  germs  capable  of  setting  up  a specific 
form  of  disease.  As  sewage  is  largely  made  up  of  this  kind  of 
matter,  it  is  a very  dangerous  form  of  pollution.  Sewer  gases 
are  also  productive  of  disease,  (31)  especially  when  the  atmosphere 
is  heavy,  as  it  then  favors  the  accumulation  of  the  products  of 
decomposition  and  the  production  of  germs.  Wherever  Bacteria 
are  found  abundantly,  decomposing  nitrogenous  organic  matter  is 
always  present;  and  Pasteur  has  shown  that  Bacteria  do  not  multiply 
without  a putrefactive  environment,  but  remain  infertile  until  they 
perish.  These  germs  only  flourish  in  a neutral  or  alkaline  mens- 
trum,  such  as  is  produced  by  decomposing  sewage  matter,  when 


(31)  Report  of  Michigan  State  Board  of  Health,  1885,  pp.  64-65. 


— 17 — 


aided  by  heat,  and  all  standard  authorities  agree  that  these  alkaline 
waters  are  dangerous  for  drinking  purposes.  Water  which  contains 
an  excessive  quantity  of  the  alkaline  carbonates  tends  to  make  the 
system  alkaline,  and  physicians  often  find  it  necessary  to  put 
patients  suffering  with  digestive,  intestinal,  and  renal  diseases,  upon 
distilled  water  as  a beverage,  and  with  happy  effects. 

In  the  healthy  human  system  germs  do  not  thrive,  as  the  reaction 
therein  is  acid.  But  in  persons  afflicted  with  digestive  disorders,  in 
which  the  gastric  juice  is  restrained,  pathogenic  germs  find  a fertile 
soil  and  muliply  with  inconceivable  rapidity.  A free  supply  of 
gastric  juice  will  kill  and  digest  them.  (32)*  A good  corrective  for 
alkaline  polluted  waters  is  sulphuric  acid.  This  arrests  putrefaction 
and  destroys  the  germs.  Workmen,  whose  employment,  location 
and  habits,  favor  an  attack  of  zymotic  disease,  sometimes  prevent 
an  epidemic  by  drinking  water  acidified  with  one  or  two  drops  of 
sulphuric  acid  per  pint  of  water.  (33)  Sulphuric  acid  is  also  often 
used  with  great  advantage  in  treating  cases  of  Cholera  and  Typhoid 
Fever,  by  giving  ten  to  thirty  drops  of  acid  in  water  three  times 
a day.  Hydronaphthol  is  aiso  recommended  as  a corrective  for 
polluted  water;  it  is  a powerful  germicide  and  is  harmless  to  the 
human  system.  Pyridine,  a constituent  of  tobacco  smoke,  is 
also  a powerful  destroyer  of  Bacteria.  It  is  a fact  worthy  of  notice 
that  men  who  use  tobacco  are  less  susceptible  to  zymotic  infection 
that  those  who  do  not  use  it,  and  that  women  are  more  frequently 
attacked  with  Diphtheria  and  Typhoid  Fever  than  men. 

In  the  production  of  contagious  and  infectious  diseases,  it  appears 
that  the  organic  matter  throws  the  Bacteria  into  a state  of  excite- 
ment in  which  they  seize  upon  the  membranes  of  the  body  and  de- 
velop the  functional  disturbance  known  as  disease,  and  this  disturb- 
ance is  in  proportion  to  the  degree  of  pollution  of  the  water;  while 
in  pure  water  the  Bacteria  remain  in  a latent  condition.  (34)  Slightly 

(32)  The  Sanitary  Era,  October  1, 1888,  p.  76. 

(33)  Report  of  Examination  of  Water  from  the  River  Schuylkill,  Cresson,  pp.  13-14. 

(34)  Report  of  Connecticut  State  Board  of  Health,  1886,  pp.  294-298;  Reports  of  Kansas 
State  Board  of  Health,  1886,  pp.  228-235;  and  1887,  p.  303. 

2 


-18- 


contaminated  water  often  produces  zymotic  diseases  in  weakly  per- 
sons, while  persons  of  robust  health  may  withstand  its  action.  But 
it  is  impossible  to  banish  disease  from  a town  whose  water  supply 
has  been  even  slightly  contaminated  with  the  dejections  from  fever 
patients,  as  the  weakly  inhabitants  will  contract  the  disease  first, 
from  the  almost  inappreciable  amount  of  infection  contained  in  the 
water,  and  from  them  the  disease  will  spread  to  those  who  have 
resisted  its  action  in  a diluted  condition. 

VI.  WATER  SUPPLIES. 

Rain-water. — There  is  a popular  idea  that  rain-water,  as  it  falls, 
is  perfectly  free  from  impurities;  but  in  fact,  the  first  fall  of  rain 
after  a drouth  is  swarming  with  living  organisms,  which  multiply 
and  perish,  polluting  the  water  with  the  products  of  their  decom- 
position. Even  the  purest  air  contains  myriads  of  motes  which  can 
be  seen  in  the  sunbeam  with  the  naked  eye,  and  they  are  washed 
from  the  air  by  the  descending  rain.  The  exhalations  which  rise 
from  decomposing  organic  matter,  and  float  in  the  atmosphere,  are 
also  carried  down  in  the  rain  or  even  humid  air,  so  the  first  rain 
that  falls  during  a storm  is  always  more  or  less  impure,  and  unfit 
for  drinking  purposes;  but  the  air  becomes  purified  in  a short  time, 
and  the  rain  that  falls  thereafter  is  approximately  pure  water. 
v The  British  Bivers  Pollution  Commissioners  concluded  that  4 4 half 
a pint  of  rain-water  often  condenses  out  of  about  three  thousand 
three  hundred  and  seventy-three  cubic  feet  of  air,  and  thus  in  drink- 
ing a tumbler  of  such  water,  impurities,  which  would  only  gain 
access  to  the  lungs  in  about  eight  days,  are  swallowed  at  once.”(35) 
These  impurities  consist  of  ammoniacal  salts,  nitrous  and  nitric  acids, 
sodium  chloride,  calcium  compounds,  and  organic  matter;  and  the 
solid  impurities  usually  amount  to  two  or  three  grains  per  gallon. 
And  when  the  water  has  drained  from  the  roofs  of  buildings,  after 
a dry  season,  the  . additional  impurities  consist  of  dust,  dead  insects, 
excreta  of  birds,  and  probably  dried  disease  germs.  As  the  rain 
falls,  it  becomes  thoroughly  aerated;  but  rain-water  has  usually  a 


(35)  Potable  Water,  Ekin.  p.  9. 


—19— 


Eat,  smoky  taste,  caused  by  the  absence  of  carbonic  anhydride  and 
alkaline  salts. 

In  some  of  the  southern  cities,  (36)  near  the  Gulf  of  Mexico,  where 
it  is  impossible  to  secure  a supply  of  pure  well  or  spring-water, 
rain-water  is  used  extensively  for  domestic  purposes.  It  is  very 
important  in  the  construction  of  cisterns  for  storage  of  drinking 
water  that  great  care  should  be  exercised  in  preparing  the  walls 
against  any  leakage  from  cess-pools  and  privies.  Rain-water,  when 
collected  toward  the  end  of  storms  and  properly  filtered  through 
sand  and  charcoal,  is  perfectly  wholesome,  provided  there  is  no 
drainage  into  the  cistern. 

Well-water. — The  purity  of  well-water  depends  mainly  upon  the 
depth  and  situation  of  the  well,  and  the  nature  of  the  surrounding 
soil.  Deep  wells,  when  properly  made,  are  generally  free  from 
organic  impurities,  but  their  waters  are  impregnated  with  harden- 
ing salts.  Artesian  well-water  is  also  free  from  organic  impurities, 
but  it  is  usually  highly  mineralized.  Deep  well-waters  are  not 
best  suited  to  the  digestive  powers  of  man;  and  every  intelligent 
groom  and  herdsman  knows  that  such  waters  are  also  more  preju- 
dicial to  horses  and  cattle  than  even  the  water  of  a muddy  stream. 

The  abundance  of  filth  in  densely  populated  cities  renders  the 
soil  unfit  for  the  filtration  and  storage  of  water,  and  surface  wells 
in  such  soil  furnish  only  a polluted  and  dangerous  supply,  as  the 
water  is  not  sufficiently  aerated  for  the  oxidation  of  its  organic 
matter.  These  wells  are  frequently  situated  in  too  close  proximity 
to  dwellings,  stables,  cess-pools,  privy-vaults,  and  other  sources  of 
pollution,  and  they  are  thus  frequently  important  factors  in  dissem- 
' mating  disease. 

Rain-water,  as  it  passes  into  the  earth,  extracts  from  the  surface 
soil  great  quantities  of  impurities,  like  decaying  vegetation  and  the 
filth  and  excrement  of  animals,  which  it  carries  down  into  the  cir- 
culating currents,  and  it  often  happens  that  the  drainage  of  cess- 
pools and  privies  finds  a direct  channel  into  the  well.  The  germs 
from  diseased  patients  thus  find  their  way  to  the  water  supply,  and 


(3®)  Report  of  Connecticut  State  Board  of  Health,  1885,  pp.  254-255. 


—20— 


many  surface  wells  are  nothing  more  than  receptacles  for  diluted 
excrementitious  matter. 

It  is  said  that  the  circulation  of  water  is  so  thorough  in  the  earth 
that  if  a barrel  of  kerosene  oil  be  placed  ten  feet  under  ground,  every 
well  within  a quarter  of  a mile  will  be  contaminated,  and  the  oil 
will  be  apparent  to  the  taste.  (37)  It  has  been  demonstrated  that  in 
compact  soils,  the  level  of  the  ground  water  is  influenced  by  pump- 
ing, for  a distance  of  two  hundred  feet  in  all  directions  around  a 
well,  while  in  loose,  gravelly  soils,  the  circle  of  influence  may  have 
a radius  of  more  than  two  thousand  feet.  (38)  This  produces  a cir- 
culation of  water  toward  the  center,  and  consequently  a washing  of 
the  filth  of  the  soil  into  the  well.  No  stable,  cess-pool,  privy-vault, 
or  other  source  of  contamination  should  be  within  this  radius. 

Many  severe  outbreaks  of  epidemic  diseases  have  been  traced  to 
the  use  of  surface  well-water  in  cities,  and  there  is  strong  reason 
to  believe  that  sporadic  attacks  oi  Typhoid  Fever  often  occur  in 
isolated  country  homes  from  the  same  cause.  When  scientific  views 
concerning  the  pollution  of  well-waters  are  disseminated,  surface 
wells  will  be  rapidly  abandoned  by  the  intelligent  classes. 

In  the  ordinary  method  of  bricking  or  walling  a well,  no  protec- 
tion is  offered  against  surface  drainage,  and  a deep  well  thus  con- 
structed is  no  better  than  a surface  well.  Open  wells  should  always 
be  walled  with  hydraulic  cement  above  the  water  line,  to  prevent 
the  admission  of  filth.  Surface  contamination  is  also  prevented  by 
the  use  of  deep  “ drive-wells  with  these  the  only  pollution  comes 
from  the  downward  circulating  currents.  Wooden  curbing  for 
wells  is  a serious  source  of  danger,  as  the  wood  soon  becomes 
rotten,  contaminates  the  water,  and  promotes  the  growth  of  fungi. 

Spring- water. — Springs  are  fountains  of  water  which  flow  from 
subterranean  channels.  This  term  is  sometimes  incorrectly  applied 
to  mere  shallow  pits,  filled  with  water  oozing  from  marshy  sur- 
roundings, and  with  little  or  no  visible  outflow.  The  water  which 
gathers  into  the  subterranean  channels  descends  from  the  earth’s 
surface;  and  if  the  surface  water  is  polluted,  the  springs  which 


(37)  Water,  Moore,  p.  31. 

(38)  Water  Supply,  Nichols,  pp.  109-114. 


—21— 


receive  their  supplies  from  it  are  liable  to  be  impure.  The  organic 
constituents,  in  filtering  through  the  earth,  oxidize  to  harmless  in- 
organic products,  if  the  filtering  bed  is  sufficiently  deep;  but  disease 
germs  are  not  thus  destroyed. 

Spring-water  which  flows  from  hill  or  mountain  sides  is  generally 
cold,  and  has  a uniform  temperature  the  year  around.  Springs  are 
also  superior  to  wells  on  account  of  their  freedom  from  the  accumu- 
lated matter  which  is  always  found  on  the  surface  of  well-waters. 

Average  porous  soil  contains  about  two  hundred  and  fifty  times 
as  much  carbonic  anhydride  as  does  air,  and  this  is  taken  into  the 
percolating  water  as  it  filters  into  the  subterranean  channels,  and  it 
renders  the  water  especially  palatable.  It  is  this  carbonic  anhydride 
in  water  which  dissolves  limestone,  converting  it  into  soluble  bicar- 
bonates. 

It  is,  therefore,  evident  that  springs  furnish  us  the  best  water,  as 
they  are  generally  free  from  organic  pollution,  and  their  waters  are 
very  palatable  from  the  gases  held  in  solution.  “A  perfectly  pure 
spring-water  is  certainly  the  most  healthy  beverage  in  the  world. 
Such  waters  are  abundant,  and  can  now  be  easily  obtained.  It  will 
be  a happy  day  for  us  all  when  their  use  shall  have  become  general 
or  universal  for  drinking  purposes.  ”(39) 

River  cmd  Lake-water. — Rivers  are  the  natural  drains  of  the  ter- 
ritory through  which  they  flow,  being  fed  by  smaller  streams, 
springs,  rains  and  surface  drainage.  “They  are  the  receptacles  of 
all  the  waste  products  of  the  inhabitants  of  the  district;  they  receive 
the  contents  of  sewers,  cess-pools  and  privies;  the  offal  of  distiller- 
ies, slaughter-houses  and  tanneries,  and  the  refuse  of  factories. 
Into  them  are  thrown  carcasses  of  dead  animals,  as  the  most  expe- 
ditious method  of  burial.  From  swamps  they  receive  the  matter 
of  vegetable  decomposition,  and  are  discolored  by  flowing  over 
beds  of  peat.”(40)  The  factories  that  are  especially  objectionable 
are  dye  works,  sugar  refineries,  starch  works,  and  glucose  works. 
Rivers  are  also  sometimes  polluted  by  the  filth  from  stock  yards. 

The  Prussian  government  protects  its  public  water  supplies  by 


(39)  Hand-book  for  Water  Drinkers,  Austin,  p.  13. 

(40)  Water  Supply,  Dickinson,  p.  5. 


-22- 


forbidding  the  discharge  of  sewage  into  its  rivers.  Many  of  the 
organic  substances  which  are  washed  into  rivers  from  cities  situ- 
ated on  their  banks,  undergo  decomposition,  and  give  rise  to  pro- 
ducts, some  of  which  have  the  power  to  produce  disturbances  in 
the  human  system,  and  others  to  propagate  the  germs  of  disease. 

River-water,  below  the  discharge  of  city  sewage,  is  a filthy  and 
dangerous  beverage,  and  notwithstanding  its  natural  purification 
by  sunlight,  by  oxidation  and  by  living  organisms,  it  may  never 
become  free  from  disease  germs.  A stream  which  has  received  much 
filth  in  its  course,  should  be  considered  objectionable  for  domestic 
use,  unless  the  volume-ratio  of  the  filth  to  the  water  is  inapprecia- 
bly small.  The  pollution  of  streams  in  rural  districts,  from  the 
decay  of  vegetation,  is  always  greatest  in  the  Fall,  and  that  from 
suspended  matter,  is  always  greatest  in  the  Spring. 

River-water  originating  in  mountainous  districts  is  unquestionably 
the  best  for  city  supplies,  as  under  ordinary  conditions  it  is  softer 
than  well  or  spring-water,  and  it  is  freer  from  organic  and  living 
matter  than  surface  wells  and  stagnant  lakes  and  ponds.  The 
objections  that  are  offered  against  the  use  of  river-water  are  on 
account  of  its  high  temperature,  frequent  turbidity,  and  its  liability 
to  contamination;  and  it  is  true  that  some  rivers  furnish  water  only 
fit  for  hydrant  and  manufacturing  purposes.  But  by  the  use  of  ice, 
efficient  systems  of  purification,  and  proper  precautions  against 
pollution,  river-waters  are  generally  excellent  supplies  for  cities 
and  towns,  where  an  abundance  of  pure  water  is  needed.  In  the 
deep-well  system  for  the  purification  of  water,  the  wells  receive 
only  a part  of  their  water  from  the  river,  on  whose  bank  they  are 
situated,  as  the  ground-water  is  constantly  flowing  toward  the  river 
channel. 

Lakes  are  the  reservoirs  into  which  rivers  and  other  streams 
empty,  and  their  waters  are  not  widely  different  from  their  sources 
of  supply.  These  great  bodies  of  water  remain  cold  during  Sum- 
mer, and  they  become  somewhat  purer  by  the  sedimentation  of 
their  suspended  matter.  Pond-water  often  becomes  unfit  for 
domestic  use,  from  the  growth  of  Algce  and  fresh  water  Sponges . 


—23— 


VII.  NATURAL  PURIFICATION. 

Streams  are  partially  purified  by  the  sedimentation  of  their  sus- 
pended matter (41)  which  takes  place  as  the  velocity  of  the  current 
diminishes.  A stream  which  is  very  turbid  after  a heavy  rain  may 
soon  become  clear,  owing  to  its  diminishing  velocity,  and  the- 
insoluble  matter  either  sinks  to  the  bottom  or  is  precipitated  along 
the  banks.  The  retarding  influence  of  tidal  waves  also  assists  in 
the  precipitation  of  suspended  matter;  and  Barus(42)  has  shown 
that  the  sedimentation  of  fine  particles  is  promoted  by  the  action 
of  salt  water,  so  there  is  a rapid  precipitation  of  silt  where  rivers 
enter  the  sea.  As  the  mineral  matter  subsides,  it  generally  carries 
down  with  it  much  of  the  flocculent,  organic  matter  that  would 
otherwise  remain  in  suspension  for  many  days. 

An  apparent  purification  of  polluted  water  is  effected  by 
dilution,  and  the  self-purification  of  many  streams  is  largely  due  to 
this  cause.  Some  of  the  chemical  waste  products  of  factories, 
when  poured  into  rivers  in  large  quantities,  are  sufficient  to  render 
the  water  wholly  unfit  for  domestic  use,  but  in  the  course  of  a few 
miles  the  pollution  becomes  so  much  diluted  that  the  water  is 
rendered  harmless.  In  some  cases,  however,  these  products  fur- 
nish a rank  growth  of  Algos , and  the  water  is  thereby  rendered  so 
objectionable  that  even  fish  cannot  survive  in  it.  This  is  the  case 
with  the  Iowa  River  pollution.  (43) 

The  mineral  impurities  of  streams  are  sometimes  removed  by 
mingling  their  waters  with  other  streams  of  a different  nature,  or 
by  flowing  over  rocks  which  act  chemically  upon  them.  This  is 
beautifully  illustrated  in  the  purification  of  the  Schuylkill  River 
before  it  reaches  Philadelphia.  (44)  This  river  receives  the  drain- 
age from  many  mines,  and  is  in  its  upper  course  highly  charged 

(41)  “ The  water  of  the  Mississippi  contains  forty  grains  of  mud  per  gallon;  and  it  is 
estimated  that  this  river  carries  four  hundred  million  tons  of  sediment  per  annum 
into  the  Gulf  of  Mexico.  The  Ganges  is  said  to  carry  down  six  billion,  three  hundred 
and  sixty-eight  million  cubic  feet  annually.” — [Report  of  American  Public  Health 
Association,  Vol.  I,  p.  536.] 

(42)  Bulletin,  No.  36,  United  States  Geological  Survey. 

(43)  Monthly  Bulletin,  Iowa  State  Board  of  Health,  July.  1889. 

(44)  Examination  of  Water  for  Sanitary  and  Technical  Purposes,  Leffmann  and 

Beam,  pp.  10-11. 


— 24r~ 


with  iron  salts  and  free  mineral  acids,  and  its  water  is  unfit  for 
domestic  and  manufacturing  purposes.  In  its  course,  the  river 
passes  through  an  extensive  limestone  district,  and  into  it  are 
emptied  several  large  streams,  highly  charged  with  calcium  bicar- 
bonate. The  free  acids  are  thus  completely  neutralized,  and  the 
iron  and  much  of  the  calcium  are  precipitated.  At  Philadelphia 
the  water  is  soft  and  superior  to  the  water  at  the  source  of  the  river 
or  at  the  middle  Schuylkill  region,  as  it  contains  only  traces  of 
iron  and  a small  amount  of  calcium  sulphate. 

Running  water,  especially  when  it  flows  over  cataracts  or  is  thor- 
oughly agitated  in  the  air,  absorbs  oxygen  to  such  an  extent  that 
its  organic  matter  becomes  rapidly  oxidized;  and  the  purification  of 
water  is  also  greatly  promoted  by  the  agency  of  sunlight.  This  is 
one  of  nature’s  most  efficient  methods  of  self -purification,  and  1 c the 
pure  water  of  mountain  streams  and  swiftly-running  brooks  and 
rivers  owe  their  freedom  from  organic  impurities  largely  to  their 
continued  and  violent  contact  and  admixture  with  atmospheric 
air.”(45)  Some  organic  substances  easily  oxidize  into  ammonia, 
nitrites,  nitrates,  and  carbonic  anhydride,  while  others,  like  muscu-. 
lar  fibre,  may  remain  for  months  in  water,  and  still  be  recognizable 
under  the  microscope.  These  chemical  changes  take  place  most 
rapidly  in  Summer,  owing  to  the  favorable  conditions  of  heat,  light 
and  motion;  but  in  Winter  the  oxidation  is  retarded  by  the  low  tem- 
perature and  the  ice  formations  which  shut  out  the  light  and  air  and 
impede  the  motion  of  the  water. 

The  pollution  of  English  streams  is  carried  to  such  an  enormous 
extent  that  the  waters  of  many,  where  city  sewage  enters  them,  are 
actually  offensive.  In  their  course,  the  water  and  banks  become 
blackened  from  the  formation  of  sulphide  of  iron,  and  with  this 
formation  the  Sewage  Fungus  appears.  Further  on  in  their  course, 
the  black  color  of  the  water  and  the  Fungus  decrease  and  disappear, 
and  in  their  place  vegetation  is  luxuriant,  fish  abound,  and  the 
water  becomes  clear  and  apparently  pure,  from  its  dilution  and  oxi- 
dation, and  from  the  agency  of  vegetable  and  animal  life.  The 


(*5)  Water  Supply  of  U.  S.  Capitol,  49th  Congress,  1st  Session,  Ex.  Doc.  No.  154.  p.  20. 


-25- 


distance  which  running  water  requires  for  its  apparent  purification, 
depends  mainly  upon  the  extent  and  nature  of  its  pollution,  the 
inflowing  streams,  and  the  agitation  of  the  water  in  its  course,  and 
it  is  safe  to  say  that  it  generally  requires  from  five  to  twenty 
miles.  (46) 

But  self-purification  is  no  guarantee  that  running  water  is  per- 
fectly wholesome  at  any  distance  below  a point  where  it  was  cer- 
tainly polluted  with  the  contents  of  sewers  and  privy-vaults,  or  the 
products  of  decomposition  of  vegetable  and  animal  matter.  The 
question,  to  what  extent  must  impure  water  be  diluted  or  oxidized 
to  render  it  safe  for  domestic  purposes,  cannot  be  answered.  Mere 
dilution  of  polluted  water  does  not  render  inoperative  the  action  of 
living  Bacteria , owing  to  the  marvelous  rapidity  of  their  reproduc- 
tion ; and  under  favorable  conditions,  it  requires  only  a few  days 
for  pathogenic  Bacteria  to  render  water  exceedingly  dangerous,  even 
though  in  other  respects  it  is  comparatively  pure. 

In  freezing,  water  is  partially  purified,  (47)  as  this  operation  elimin- 
ates a large  portion  of  its  suspended  matter,  but  the  inorganic  salts, 
and  the  organic  constituents,  are  only  partially  removed.  The 
experiments  of  Dr.  C.  P.  Pengra(48)  show  that  water  in  freezing  is 
only  freed  of  about  fifty  per  cent  of  its  organic  crystalloids,  twenty 
per  cent  of  its  colloids,  forty  per  cent  of  its  mineral  salts,  and 
ninety  per  cent  of  its  Bacteria.  It  is,  therefore,  evident  that  ice 
may  be  a prolific  source  of  disease,  and  many  dangerous  epidem- 
ics(49)  have  been  caused  by  it.  The  impurities  excluded  in  freezing 
remain  in  the  unfrozen  water,  in  a concentrated  and  more  danger- 
ous form,  and  this  may  in  part  explain  why  Typhoid  Fever  so  often 
prevails,  and  is  of  such  a severe  type,  during  cold  Winter  weather. 

(46)  Report  of  Massachusetts  State  Board  of  Health,  Vol.  VII,  p.  146. *  * 

*The  Royal  Commissioners  concluded,  however,  that  running  water  is  so  slowly 
purified  that  there  is  not  a river  in  England  sufficiently  long  to  dispose  of  a moderate 
amount  of  sewage,  through  natural  agencies. 

(47)  On  Bacteria  in  Ice  and  Their  Relations  to  Disease,  Prudden;  Our  Ice  Supply  and 
its  Dangers,  Prudden. 

(48)  Reports  of  Michigan  State  Board  of  Health,  1882,  pp.  48-50;  and  1884,  pp.  79-81. 

(49)  Report  of  Massachusetts  State  Board  of  Health,  Vol.  VII,  p.  465;  Report  of  Con- 
necticut State  Board  of  Health,  Vol.  II,  p.  90. 


—26— 


The  soil  may  act  as  a mechanical  purifier  of  water,  by  the  re- 
moval of  suspended  matter  as  the  water  filters  through  it,  and  as  a 
chemical  purifier,  by  its  oxidizing  and  other  chemical  action  upon 
the  organic  impurities,  whether  they  are  held  in  suspension  or  solu- 
tion. The  filtering  power  of  soil  is  found  to  vary  greatly.  (50)  Sand 
and  gravel  act  mainly  as  mechanical  filters,  while  ferric  oxide  is  the 
oxygen  carrier  of  the  soil.  In  general,  a coarse  soil  is  not  so- 
efficient  in  its  mechanical  and  chemical  action  as  a similar  finer  one; 
and  every  soil  which  has  been  charged  with  organic  inpurities  is 
unquestionably  inefficient.  Even  a good  filtering  soil  which  receives 
an  excess  of  impurities,  becomes,  at  last,  ineffective. 

Too  much  confidence,  however,  is  often  ignorantly  placed  in  the 
purifying  power  of  the  soil.  From  experiments  instituted  by  the 
National  Board  of  Health,  (51)  it  appears  that  sand  and  gravel  inter- 
pose absolutely  no  barrier  between  wells  and  the  Bacteria  of  cess- 
pools, privy-vaults,  and  cemeteries,  lying  even  at  great  distances 
from  them.  In  further  support  of  this  view,  one  celebrated  case 
will  suffice:  In  August,  1872,  an  outbreak  of  Typhoid  Fever 
occurred  at  Lausen,  near  Basil,  in  Switzerland.  (52)  The  village 
water  supply  was  from  a spring  at  the  foot  of  the  Stockhalden. 
Suspicion  was  attached  to  this  water,  for  it  was  found  that  the  six 
houses  using  well-water  were  free  from  the  disease,  but  scarcely 
one  of  the  others  escaped.  Upon  investigation  it  was  found  that 
Typhoid  Fever  had  occurred  at  a farm-house  on  the  opposite  side 
of  the  Stockhalden,  and  the  drainage  from  this  house  went  into  a 
brook,  a part  of  which  was  lost  in  the  mountain,  about  a mile  dis- 
tant from  Lausen.  Large  quantities  of  salt  were  thrown  into  the 
stream  and  the  salt  was  soon  detected  in  the  Lausen  supply,  thus 
proving  the  connection  between  the  two.  Several  hundred  pounds 
of  flour  were  then  thrown  into  the  stream,  but  not  a trace  of  it  was 
detected  in  the  water  supply,  showing  the  thorough  filtration  of  the 
water  in  passing  through  the  mountain.  The  case  was  elaborately 
investigated  by  Dr.  A.  Hagler,  of  Basil,  and  it  is  of  the  greatest 


(50)  Report  of  Michigan  State  Board  of  Health,  1876,  pp.  110-111. 

(51)  Report  of  National  Board  of  Health,  1882,  p.  582. 

(52)  Nature,  Vol.  XIII,  p.  447. 


-27- 


interest  in  showing  that  the  most  thorough  filtration  through  soil  is 
insufficient  to  remove  Typhoid  Fever  germs  from  polluted  water. 

Finally,  we  are  indebted  to  low  forms  of  life  for  much  of  the  self- 
purification of  water.  The  decomposition  of  organic  matter  is  the 
joint  work  of  a number  of  independent  organisms,  the  results  of 
one  class  following  those  of  another  until  organization  is  entirely 
destroyed. 

The  Entomostraca  and  other  low  forms  of  animal  life,  owing  to 
their  fecundity,  are  very  important  factors  in  removing  organic 
impurities  from  water.  Some  of  them  seem  to  act  mostly  as  cata- 
lytic ^agents,  producing  chemical  changes  by  which  the  noxious 
organic  constituents  are  converted  into  harmless  products. 

Notwithstanding  what  has  been  said  concerning  ^ decomposing 
Algae,  the  living  forms  of  Algae  should  not  be  considered  an  unmiti- 
gated evil,  as  most  of  them  are  really  purifying  agents,  since  they 
assimilate  the  dissolved  organic  matter  in  water.  They  also  assim- 
ilate the  carbonic  anhydride,  ammonia,  and  nitrogen  acids  produced 
by  lower  forms  of  cryptogamic  life.  The  main  function  of  Fungi 
in  the  purification  of  water  is  apparently  the  oxidation  of  organic 
carbon.  (53)  Next  of  importance  is  the  great  army  of  Bacteriay 
which  embraces  many  families  of  similar  physical  structure,  but 
the  families  are  endowed  with  very  different  chemical  powers. 
They  sweeten  water  by  a chemical  process  necessary  for  their  own 
nutrition;  and  our  water  supplies  would  become  magazines  of 
deadly  poisons,  were  it  not  for  the  myriads  of  these  micro-organisms 
which  attack  dead  organic  matter,  and  cause  its  elements  to  enter 
into  new  and  useful  combinations.  One  class  of  Bacteria  converts 
the  nitrogen  in  nitrogenous  organic  matter  into  ammonia;  another 
class  elaborates  this  ammonia  into  nitrous  and  nitric  acids;  while 
another  class  is  engaged  in  converting  organic  carbon  into  carbonic 
anhydride.  Experiments (54)  show  that  sterilization  of  polluted 
water  arrests  the  decomposition  of  its  organic  matter,  for  ozone  and 
hydrogen  peroxide  fail  to  oxidize  it;  but  when  such  water  is  sub- 
jected to  biological  agencies,  it  is. purified  as  usual.  Indeed,  it 


(53)  Report  on  the  Waters  of  the  Hudson  River,  Chandler,  January,  1885,  pp.  7-14. 
(5*)  Report  of  Kansas  State  Board  of  Health,  1887,  pp.  328-329. 


—28— 


appears  that  the  removal  of  organic  impurities  is  more  of  a biolog- 
ical than  of  a chemical  question,  and  in  considering  the  natural 
purification  of  water,  the  action  of  micro-organisms  should  have 
the  first  rank,  even  though  some  of  them  are  pathogenic. 

It  is  well  known  that  these  chemical  changes  are  more  rapidly  ef- 
fected when  the  water  filters  through  the  pores  of  the  soil,  than 
when  it  is  stagnant,  or  even  when  it  is  flowing  in  the  current  of  a 
stream.  This  is  explained  by  the  fact  that  the  purifying  Bacteria 
mainly  have  their  abode  in  the  three  or  four  feet  (&5)  of  surface  soil 
of  the  earth,  and  that  they  so  modify  the  organic  matter  of  water 
us  it  passes  through  this  layer  of  soil,  that  the  roots  of  living  plants 
can  absorb  and  assimilate  it. 


VIII.  ARTIFICIAL  PURIFICATION. 

Processes. — Water  may  be  artificially  purified  by  any  of  the  fol- 
lowing processes:  Boiling,  distillation,  aeration,  sedimentation, 
precipitation  and  filtration. 

Boiling. — By  boiling  polluted  water  for  some  time,  the  living 
organisms  in  it  are  always  partially,  and  generally  entirely  de- 
stroyed. Algce  and  Fungi  are  easily  killed  in  this  way.  Professor 
Tyndall  (56)  has  shown  that  there  are  periods  in  the  life  of  Bacteria 
when  they  can  resist  the  action  of  boiling  water;  but  as  they  soften 
before  propagation,  water  containing  them,  can  be  completely 
sterilized  by  repeated  boiling,  for  at  the  proper  time,  this  not  only 
destroys  the  Bacteria  but  it  destroys  their  spores  as  well.  In  order, 
then,  to  guard  ourselves  against  these  organisms,  polluted  water 
should  never  be  used  for  drinking  purposes,  without  first  being 
boiled  for  some  time  (two  or  three  hours),  as  this  prolonged  opera- 
tion thoroughly  sterilizes  it.  Indeed,  it  is  perhaps  true  that  the 
two  most  effective  measures  which  can  be  taken  in  avoiding  zymotic 
diseases,  consist  in  boiling  all  kthe  water  and  milk  that  we  use  for 
drinking  purposes. 

(55)  Report  of  Committee  on  the  Pollution  of  Water  Supplies,  American  Public  Health 
Association,  1888,  p.  11. 

(56)  Practical  Hygiene,  Parkes.  Seventh  Edition,  p.  79. 


—29— 


Distillation. — Water  may  be  freed  from  its  solid  impurities  by  a 
process  of  distillation.  In  this  way,  inland  bodies  of  water  and 
the  seas,  become  saline  from  the  concentration  of  their  mineral  con- 
stituents, while  water  in  its  crystalline  purity  evaporates  from  the 
surface.  In  the  first  part  of  distillation,  the  occluded  gases  are 
liberated,  and  they  pass  over  with  the  distillate.  It  has  also  been 
claimed  that  Bacteria  and  their  spores  are  carried  over  with  the  dis- 
tillate, but  the  evidence  is  very  unreliable.  The  flatness  of  distilled 
water,  which  is  always  objectionable  at  first,  is  said  to  be  preferred 
by  some  people  who  have  accustomed  themselves  to  it;  but  this  ob- 
jection can  be  partially  overcome  by  aeration.  Distilled  water  is. 
not  generally  used  for  drinking  purposes,  except  by  persons  afflicted 
with  renal  and  bladder  difficulties.  But  it  is  said  to  be  used  reg- 
ularly on  the  coast  of  Chili,  (57)  where  it  is  made  from  sea  water, 
and  it  is  used  oftentimes  on  long  ocean  voyages  and  expeditions, 
where  fresh  water  cannot  be  obtained.  As  coal  will  distill  about 
eight  times  its  weight  of  water,  there  is  an  advantage  in  conveying 
coal  instead  of  fresh  water  on  board  of  ships. 

Aeration. — Artificial  aeration  is  a process  by  which  we  imitate 
nature  in  the  purification  of  water.  This  oxidizes  organic  matter  to. 
harmless  products,  and  renders  the  water  highly  palatable.  As  a 
process,  aeration  was  introduced  by  Lind  more  than  a century  ago,, 
for  the  purification  of  water  on  the  western  coast  of  Africa.  This 
process  has  since  been  used  on  a large  scale  in  Russia,  by  allowing 
the  water  to  flow  down  a series  of  steps,  passing  through  wire- 
gauze  as  it  descends,  and  it  has  also  been  used  on  a small  scale  in 
Paris.  But  artificial  aeration  has  only  recently  been  introduced  in 
this  country  for  city  water  supplies.  In  1883,  (5S)  Professor  Albert 
R.  Leeds  demonstrated  by  laboratory  experiments,  that  the  tem- 
porary offensive  contamination  of  the  Schuylkill  water  at  Phila- 
delphia, could  be  removed  by  oxidation,  and  at  his  suggestion  the 
Philadelphia  Water  Company  removed  the  objection  by  pumping 
air  under  great  pressure  into  its  supply.  At  a subsequent  date, 
the  water  supply  of  Hoboken,  Hew  Jersey,  became  extraordinarily 


(57)  Water  Analysis,  Wanklyn  and  Chapman,  Sixth  Edition,  p.  107. 

(58)  Water,  Moore,  pp.  72-74. 


30- 


offensive  in  odor  and  taste,  and  an  examination  by  Dr.  Leeds 
showed  this  water  also  to  be  deficient  in  oxygen.  In  September, 
1886,  the  evil  was  removed . by  artificial  aeration,  and  the  impuri- 
ties were  diminished  and  vegetable  growth  ceased,  n 

The  water  of  the  Greenwood  Cemetery  Water  Works,  Brooklyn, 
~Ne w York,  some  time  since  became  nauseous  from  the  accumula- 
tion of  a greenish,  vegetable  slime.  Examination  revealed  the  fact 
that  the  water  was  deficient  in  dissolved  oxygen,  and  that  it  con- 
tained an  unusual  number  of  Diatoms.  The  problem  was,  there- 
fore, to  devise  a process  which  would  remove  the  pabulum  neces- 
sary for  their  growth.  An  amount  of  air  equal  to  one  tenth  of  the 
water,  under  a pressure  of  eighty  pounds  per  square  inch,  was 
found  sufficient  to  oxidize  the  pabulum,  and  the  water  was  rendered 
clear  and  sparkling  by  this  artificial  aeration. 

Under  great  pressure,  air  oxidizes  nitrogenous  substances  to  inor- 
organic  products,  and  it  therefore  deprives  the  minute  forms  of  life 
of  the  pabulum  on  which  they  thrive,  and  they  are  rendered  latent. 
But  it  must  not  be  understood  that  mere  aeration  effects  these  trans- 
formations, for  experiments  (59)  have  clearly  demonstrated  that 
without  the  aid  of  biological  agencies,  there  is  no  oxidation,  and 
no  purification  from  the  aeration  of  water.  Oxidation  is,  indeed, 
but  a finishing  process,  and,  therefore,  after  coagulating  and  filter- 
ing out  the  bulk  of  impurities,  a vigorous  aeration,  under  high 
pressure,  in  such  a manner  as  to  cause  the  oxygen  to  reach  every 
portion  of  the  water  should  be  effected,  and  the  oxidation  there 
completed  so  far  as  possible.  The  excessive  air  should  then  pass 
to  the  filtering  beds,  and  in  its  slow  passage  through  them  assist  in 
the  separation  and  removal  of  the  organic  impurities.  From  such 
a system  water  would  emerge  from  the  pipes  highly  charged  with 
air,  clear,  sparkling,  and  as  wholesome  as  the  best  standard  of  na- 
ture’s purified  springs. 

Sedimentation. — In  this  country,  the  water  for  city  supplies  is 
often  only  partially  purified  by  a process  of  sedimentation.  This 
process  is  frequently  used  for  the  waters  of  the  Mississippi  and 


(59)  Report  of  Kansas  State  Board  of  Health,  1887,  pp.  328-329. 


Missouri  Rivers.  The  water  is  allowed  to  remain  at  rest  for  some 
hours,  in  large,  shallow  settling  basins,  in  which  much  of  the  sus- 
pended inorganic  matter  subsides,  and  thus  mechanically  removes 
much  of  its  organic  matter;  but  owing  to  the  expense  of  construct- 
ing, maintaining  and  operating  settling  basins,  their  use  is  not 
more  extended.  Other  systems  of  greater  sanitary  merit  do  the 
work  of  purification  more  beautifully  and  to  the  satisfaction  and 
delight  of  the  water  consumers.  After  subsidence  of  the  impuri- 
ties, the  water  is  drawn  off,  and  at  regular  intervals  the  sediment  is 
removed  from  the  basins.  If  the  water  contains  finely  divided 
particles  of  clay,  then  the  subsidence  is  so  slow  that  for  purifying  pur- 
poses this  process  is  a failure,  and  the  softer  the  water  the  more 
slowly  the  sedimentation.  It  is  said  that  the  fine  argillaceous  mat- 
ter in  the  River  Rhone  requires  four  months  of  undisturbed  repose 
for  its  subsidence.  Time  is,  therefore,  an  important  element  in  the 
purification  of  water  by  this  process. 

If  the  water  is  contaminated  with  sewage,  or  with  the  decompo- 
sition products  of  vegetable  and  animal  matter,  the  sooner  it  is 
used  the  less  harm  it  will  generally  do.  uTo  detain  it  in  a settling 
basin,  especially  in  Summer,  long  enough  for  even  its  suspended 
mineral  matter  to  go  to  the  bottom,  is  to  brew  a sort  of  devil’s 
broth  out  of  the  putrescent  ingredients,  that  will  grow  more  poison- 
ous every  day  it  is  kept.”(60)  As  the  growth  of  micro-organisms 
is  prevented  or  at  least  retarded  by  the  absence  of  sunlight,  it  has 
been  found  advantageous  to  store  water,  after  sedimentation  and 
filtration,  in  covered  reservoirs.  Dr.  Percy  F.  Frankland(61)  has 
found  that  the  twenty  thousand  germs  per  cubic  centimetre  in  the 
Thames  River  water  are  reduced  to  about  four  hundred  by  subject- 
ing the  water  to  sedimentation  and  filtration;  but  from  ninety-five 
.and  five  tenths  to  ninety-eight  and  nine  tenths  per  cent  of  the  micro- 
organisms in  the  London  water  supply  are  claimed  to  be  removed 
by  filtration  alone.  (62) 


(*0)  Water,  Moore,  p.  72. 

(61)  Report  of  Maine  State  Board  of  Health,  1887,  p.  316. 

(«2,  Report  on  Water  Supply  of  East  Saginaw,  Michigan,  p.  4. 


—32— 


Precipitation. — Many  substances  have  been  found  useful  in  pre- 
cipitating the  impurities  from  water.  Among  those  that  have  been 
mentioned  are  carbon,  borax,  ferric  chloride,  potassium  perman- 
ganate, alum,  calcium  hydrate,  and  sodium  carbonate.  The  choice 
of  a substance  depends  upon  the  nature  of  the  impurities,  the  use 
of  the  water,  and  the  magnitude  and  expense  of  the  purifying  sys- 
tem. A few  points  concerning  some  of  these  substances  will  suf- 
fice. 

Ferric  chloride(63)  to  the  amount  of  two  and  one  half  or  three 
grains  per  gallon  of  water  has  been  used  successfully  in  Holland 
in  removing  argillaceous  and  finely  divided  organic  matter  from 
water.  It  is  a powerful  oxidizing  agent,  and  when  followed  by  a 
solution  of  sodium  carbonate,  it  gives  excellent  results,  as  the  car- 
bonate precipitates  the  iron,  which  entangles  and  removes  the  or- 
ganic matter. 

Potassium  permanganate  (in  solution  as  Condy’s  red  fluid)  is  an 
excellent  purifying  agent,  as  it  partially  destroys  organic  substances 
by  oxidation,  and  its  manganese  is  generally  precipitated  as  the 
binoxide,  carrying  with  it  much  of  the  suspended  matter  present. 
A yellowish  tint  is  sometimes  produced  in  the  water  by  the  finely 
divided  particles  of  oxide  of  manganese,  and  although  this  may  be 
objectionable  to  the  sense  of  sight,  it  has  perhaps  no  ill-effects  upon 
the  human  system.  This  reagent  readily  removes  any  offensive 
odor  from  water,  but  the  degree  of  oxidation  of  the  organic  matter 
depends  somewhat  upon  the  structure  of  the  organic  matter  and 
the  temperature  of  the  water.  Potassium  permanganate  is  not  a 
complete  purifier  of  water,  but  it  does  work  which  alum  cannot  do. 

Alum  has  been  used  for  centuries  in  China  and  India  to  purify 
water.  It  is  especially  efficient  with  waters  containing  calcium 
bicarbonate,  and  it  clarifies  them  by  precipitating  the  calcareous 
and  argillaceous  impurities,  and  in  their  removal  it  is  itself  precip- 
itated as  calcium  sulphate  and  aluminium  hydrate,  which  coagulate 
and  remove  the  albuminous  matter.  So  perfect  is  its  self-precipita- 
tion that  rarely  can  we  find  a trace  of  alum  in  the  filtered  water. 


(63)  Water,  Moore,  p.  76. 


-33- 


Professor  Leeds  has  shown  that  alum  has  also  the  remarkable  prop- 
erty of  removing  Bacteria  from  water.  This  is  the  coagulent  used 
in  the  Hyatt  system  of  purification.  The  amount  of  alum  used  is 
from  one  half  to  six  grains  per  gallon  of  water.  Alum  can  be 
obtained  for  one  and  one  half  to  two  cents  per  pound;  so  its  use 
under  the  most  unfavorable  circumstances  is  very  inexpensive. 

Clark’s  process  for  softening  water  by  precipitating  its  lime  as  a 
normal  carbonate,  has  been  successfully  used  in  several  European 
water  supplies,  and  also  for  private  consumers.  This  is  accom- 
plished by  adding  to  the  water  in  settling  basins  a sufficient  quantity 
of  calcium  hydrate,  in  solution,  to  completely  neutralize  the  carbonic 
acid,  and  thus  precipitate  all  the  lime  as  a normal  carbonate.  This 
carbonate  mechanically  precipitates  the  clayey  substances,  and 
effects  a nearly  complete  removal  of  the  coagulated,  gelatinous  and 
albuminous  matter,  as  well  as  a complete  removal  of  the  coloring 
matter.  Professor  Edward  Frankland  has  shown  that  Clark’s  pro- 
cess is  very  efficient  in  removing  living  organisms  from  water. 
The  completion  of  the  removal  of  lime  is  determined  by  means 
of  a solution  of  silver  nitrate.  So  long  as  the  bicarbonates  remain 
in  solution  the  silver  nitrate  gives  a white  precipitate  with  the 
water;  but  as  soon  as  the  bicarbonates  are  removed,  then  a brown- 
ish or  yellowish  precipitate  is  formed.  The  objections  offered  against 
this  system  are  that  if  organic  matter  is  present  in  large  quantity 
the  chalk  will  not  readily  precipitate;  the  expense  of  constructing 
settling  basins  is  very  great;  and  the  accumulated  chalk  needs  fre- 
quent removal  from  the  basins,  and  consequently  entails  much 
expense.  A modern  improvement  in  this  process,  known  as  the 
Porter-Clark  process,  consists  in  a remarkably  rapid  separation  of 
the  precipitate  by  means  of  a filter-press,  which  obviates  the  diffi- 
culty of  sedimentation,  and  dispenses  with  the  expensive  settling 
basins. 

Sodium  carbonate,  or  salsoda,  is  frequently  used  in  softening- 
water  for  laundry  purposes,  as  it  precipitates  the  hardening  salts  as 
normal  carbonates. 

Filtration. — The  purification  of  water  by  filtration  for  city  sup- 
plies has  become  quite  general  in  Europe  and  most  parts  of  the 
3 


— 31— 


United  States.  The  essential  object  attained  in  this  method,  when 
the  water  is  to  be  used  for  domestic  purposes,  is  the  removal  of  the 
pabulum  or  infectious  matter,  on  which  disease  germs  multiply  and 
develop.  Experience  shows  that  this  is  best  effected  by  first 
coagulating  and  filtering  out  the  organic  matter,  in  part,  and  then 
complete  its  removal  by  rapid  oxidation  under  high  pressure.  A 
large  per  cent  of  the  Bacteria  are  thus  removed  in  filtering,  and  the 
remaining  few  are  rendered  latent,  and  the  water  becomes  harmless 
and  palatable. 

A filter  should  not  only  be  capable  of  arresting  suspended  matter, 
but  also  all  substances  in  solution  which  are  physically  or  chemically 
dangerous,  and  it  should  so  retain  them  that  the  water  cannot  wash 
them  out  again.  It  should  also  be  so  constructed  that  it  can  be  used 
for  some  time  without  deteriorating  the  quality  of  the  water. 

Filtration  effects  purification  in  three  distinct  ways: 

1.  By  straining,  in  which  the  efficiency  and  rapidity  of  the 
operation  depends  upon  the  size  of  the  pores. 

2.  By  adhesion  of  the  impurities  to  the  filtering  substances,  in 
which  the  efficiency  depends  upon  the  nature  of  the  filters,  and  the 
relative  surface  of  the  filter  pores  to  the  water  filtered. 

3.  By  sedimentation  within  the  pores  of  the  filter,  and  the 
efficiency  here  depends  upon  the  size  of  the  porous  cavities  and  the 
rate  of  filtration. 

Professor  Edward  Frankland,  of  the  Royal  Commission,  has 
thoroughly  investigated  the  efficiency  of  the  various  methods  of 
purifying  water,  and  the  following  are  the  results  of  his  observa- 
tions upon  filtration  :(64) 

1.  A proper  filtration  may  entirely  deprive  water  of  its  living 
organisms. 

2.  By  storing  water  in  receptacles  which  are  biologically  unclean, 
living  organisms  may  be  introduced  and  rapidly  multiplied. 

3.  Filters  lose  their  efficiency  by  constant  use,  and  instead  of 
removing  Bacteria , they  finally  increase  the  number  of  these 
organisms. 


(64)  Journal  of  the  Society  of  Chemical  Industry,  December,  1885. 


35— 


4.  Some  substances  which  manifest  no  chemical  action  on  water, 
are  very  successful  agents  in  removing  living  organisms  from  it. 
Such  are  charcoal  and  coke. 

5.  The  best  results  are  attained  when  the  filtering  substances  are 
frequently  removed. 

6.  What  is  gained  in  the  rapidity  of  filtration  is  lost  in  its 
efficiency. 

Sand  is  the  material  most  frequently  used  in  filtering-beds, 
although,  compressed  sponge,  animal  and  wood  charcoal,  coke, 
brick,  porous  tiles,  unglazed  earthenware,  sandstone,  (C5)  carbide  of 
iron,  and  spongy  iron  have  been  suggested. 

Animal  and  wood  charcoal,  coke  and  spongy  iron  are  the  only 
substances  which  can  be  relied  upon  for  the  removal  and  destruc- 
tion of  organic  matter.  Charcoal  condenses  oxygen  in  its  pores, 
and  as  water  passes  through  it  the  organic  matter  is  rapidly  and 
powerfully  oxidized,  the  charcoal  acting  as  a catalytic  agent.  But  it 
is  necessary  that  charcoal  filters  be  frequently  removed  and  exposed 
to  the  air,  or  sometimes  reburnt,  that  they  may  become  purified 
and  absorb  a fresh  supply  oxygen,  for  a filter  that  is  kept  constantly 
in  use  soon  become  worthless. 

Dr.  Percy  F.  Frankland  has  found  that  powdered  coke  as  a filter- 
ing material  completely  removes  micro-organisms  from  water;  and 
Salamon  and  Matthews  (66)  have  further  shown  that  the  action  of 
the  coke  is  due  mainly,  if  not  entirely,  to  the  presence  of  iron. 

In  constructing  filters  for  cisterns,  care  should  be  taken  to  so 
arrange  the  parts  of  the  filter  that  all  organic  matter  possible  may 
be  removed,  and  that  no  color  may  appear  in  the  water.  For  this 
purpose  the  conducting  pipe  from  the  roof  should  lead  directly  to 
the  filtering  box,  in  which  there  should  be  layers  of  charcoal, 
gravel,  and  sand  of  such  a thickness  as  to  effect  this  purification. 
The  water  should  only  flow  into  cisterns  during  the  Winter  and 
Spring  months,  when  the  atmosphere  is  clear  and  the  rain  pure. 

(65)  “ The  Japanese  use  porous  sandstone  hollowed  into  the  form  of  an  eg g,  and  set  in  a 
frame  over  a vessel,  into  which  the  water  drops  as  it  percolates  through  the  stone.  The 
Egyptians  adopt  the  same  method  for  clarifying  the  water  of  the  Nile.”— [American 
Cyclopaedia,  Second  Edition,  Revised,  p.  189.] 

(66)  Journal  of  the  Society  of  Chemical  Industry,  1885,  p.  261. 


—36— 


The  filters  should  be  cleansed  at  least  once  a year.  Under  proper 
management  a supply  of  pure,  cold,  cistern  water  may  always  be 
at  hand.  Cisterns  are  sometimes  constructed  in  two  vertical  com- 
partments, separated  from  each  other  by  a porous  brick  partition, 
laid  in  hydraulic  mortar.  The  water  is  allowed  to  flow  directly  into 
one  of  the  compartments,  and  filter  through  the  brick  wall  into  the 
other,  from  which  it  is  drawn  for  use.  At  first,  this  is  a very  suc- 
cessful means  of  Alteration,  but  the  partition  soon  becomes  charged 
with  impurities,  and  finally  does  more  for  contamination  than  for 
purification. 

Any  filtering  medium,  like  sand,  and  uncompressed  charcoal  and 
coke,  which  has  pores  larger  than  one  twenty-five  thousandth  of 
an  inch  in  diameter,  cannot  successfully  mechanically  remove 
Bacteria  from  water.  But  Pasteur  has  devised  a sanitary  filter 
which  eminent  authorities  claim  is  germ-proof.  The  filtering 
material  in  this  is  a fine  porcelain  imported  from  France.  These 
filters,  which  are  only  suitable  for  domestic  purposes,  consist  of 
two  concentric  tubes,  the  outer  one  being  connected  with  the  water 
pipe,  and  the  inner  tube  is  the  porcelain  filter.  The  water  is 
admitted  to  the  anular  space  between  the  two  tubes,  and  it  filters 
through  into  the  central  space,  from  which  the  clear,  sparkling 
water  is  drawn.  These  filters  are  so  constructed  that  they  can  be 
easily  and  daily  cleansed.  Other  forms  of  sterilizing  filters  are  in 
use,  but  the  writer  is  not  prepared  to  attest  to  their  efficiency. 

Systems  for  central  filtration. — One  of  the  simplest  and  cheapest 
methods (67)  of  securing  filtered  water  for  city  supplies  is  to  sink 
wells  or  pits  to  a depth  of  ten  to  forty  feet  into  the  soil,  near  the 
bed  of  a river  or  lake,  and  from  them  pump  the  water  for  general 
distribution.  These  wells  are  inclosed  with  iron  or  masonry  walls, 
which  prevent  an  influx  of  surface  soil-water.  The  river  or  lake 
water  only  enters  them  at  the  bottom,  and  it  is  thus  subjected  to 
filtration  through  natural  soil.  These  wells  generally  receive  a 
portion  of  their  supply  from  the  ground-water,  and  if  this  flows 
from  underneath  a densely-populated  city  it  is  liable  to  be  impure. 
But  this  system  gives  satisfactory  results  wdien  the  wells  are  sunk 


(67)  Water  Supply,  Dickinson,  pp.  10-11. 


below  an  impervious  stratum,  for  this  separates  the  surface  water 
•of  the  city  from  the  influx  to  the  well. 

In  the  Filter-bed  system(68)  the  basins,  as  usually  constructed,  are 
from  ten  to  sixteen  feet  in  depth.  Their  size  varies  from  twenty 
thousand  to  one  hundred  and  fifty  thousand  square  feet,  and  is 
determined  by  estimating  that  ninety  gallons  of  water  can  be  filtered 
per  day  through  each  square  foot  of  surface.  These  basins  are 
made  water-tight  by  masonry,  concrete  or  puddled  clay  walls.  In 
the  bottom  are  radiating  drains,  upon  which  is  a layer  of  broken 
stone  some  two  feet  in  thickness;  then  layers  of  coarse  gravel,  fine 
gravel,  and  finally  the  true  filter,  which  is  a layer  of  fine  sand, 
from  one  to  four  feet  in  thickness.  The  water  is  kept  from  one  to 
four  feet  in  depth  abof e the  filters,  and  it  is  purified  in  its  down- 
ward passage  through  the  sand,  and  flows  through  the  drains  to  a 
clear-water  basin.  When  the  filters  become  clogged  the  water  is 
drawn  below  the  surface  of  the  sand,  and  a layer  of  sand  from  one 
half  to  three  fourths  of  an  inch  in  thickness  is  removed,  together 
with  the  debris  which  has  accumulated  on  its  surface.  This  prac- 
tice is  continued  until  the  sand  becomes  too  thin  for  efficient  filtra- 
tion, and  then  a new  filtering-bed  is  prepared.  This  system  is  espec- 
ially applicable  to  the  purification  of  river-water,  but  the  sand  only 
acts  as  a mechanical  strainer. 

In  the  Bishof  system  the  sand  of  the  filtering  bed  is  mixed  with 
a prepared  spongy  iron,  which  is  said  to  successfully  remove  organic 
matter  from  the  water,  and  thus  render  it  wholesome.  If  the  water 
contains  a large  amount  of  fine  sand,  a preparatory  filtration  is 
necessary,  and  if  there  is  also  a large  amount  of  salts  in  solution, 
then  the  water  is  liable  to  be  impregnated  with  salts  of  iron  derived 
from  the  filtering-bed. 

The  Anderson  system,  so  successfully  used  in  purifying  the 
Antwerp  water  supply,  consists  in  passing  the  water  slowly  through 
revolving  iron  cylinders,  having  inside  projecting  shelves.  These 
cylinders  are  about  two  thirds  filled  with  iron  borings,  and  are 
slowly  revolved,  so  that  some  of  the  iron  passs  into  solution  as 


(68)  Water  Supply  of  U.  S.  Capitol,  49th  Congress,  Ex.  Doc.  No.  154,  pp.  13-15. 


—38— 


ferrous  hydroxide.  Every  particle  of  the  water  passing  through 
the  cylinder  is  thus  brought  into  direct  contact  with  the  iron,  and 
the  ferrous  hydroxide  successfully  removes  the  odor  from  the  water 
and  precipitates  the  organic  matter,  which  is  removed  by  filtering 
through  sand,  and  in  filtering,  the  ferrous  salt  is  oxidized  and  re- 
moved. Professor  Edward  Frankland  has  shown  that  prolonged 
agitation  with  solid  particles  in  the  water  completely  destroys  the 
living  organisms;  but  the  Anderson  process,  at  Antwerp,  only  par- 
tially sterilizes  the  water.  The  quantity  of  nitrogen  is  reduced  to 
one  half  or  one  third  the  amount  which  the  water  originally  fur- 
nished.  At  Antwerp,  the  time  required  for  the  water  to  pass 
through  the  cylinder  is  about  three  and  one  half  minutes,  and  for 
the  completion  of  the  purification,  about  six  hours. 

The  Tweeddale  system,  (69)  devised  by  Col.  William  Tweeddale, 
of  Topeka,  Kansas,  has  proved  very  efficient  on  a small  scale,  and 
gives  promise  of  great  satisfaction  for  the  purification  of  city  water 
supplies.  The  lime  is  precipitated  as  in  the  Clark  process;  then  a 
sufficient  quantity  of  carbonate  of  iron  is  added  to  render  insoluble 
the  organic  matter.  If  the  water  is  hard  and  clear,  a small  quantity 
of  clay  is  then  added.  The  water  is  then  violently  agitated  by 
means  of  an  air  injector,  after  which  the  water  is  allowed  to  stand 
for  ten  minutes  to  complete  the  reaction.  The  water  is  again 
violently  agitated  from  fifteen  to  twenty-five  minutes,  after  which 
the  impurities  are  allowed  to  settle,  and  the  water  is  removed  by 
decantation.  The  impurities  must  be  frequently  removed  from  the 
tanks.  The  time  required  for  the  clarification  by  this  process,  is 
from  three  to  four  hours.  In  this  system  the  water  is  softened,  the 
organic  matter  is  largely  precipitated  and  the  balance  oxidized  to 
inorganic  salts,  while  the  living  organisms  are  mostly  destro}Ted. 

In  the  Hyatt  system  of  purification,  the  inconvenience  and  dif- 
ficulty attending  the  frequent  removal  of  sediment  and  sand  in  the 
previous  methods,  are  obviated.  In  this  system  the  filters  can  be 
easily,  cheaply  and  thoroughly  cleansed.  The  impurities  are  coag- 
ulated by  means  of  alum,  and  the  water  then  passes  to  the  steel  fil- 
tering chamber  where  they  are  removed.  This  is  a vertical  cylinder, 


(69)  Report  of  Kansas  State  Board  of  Health,  1887,  pp.  330-331. 


-39- 


having  a diameter  nearly  twice  its  height.  Through  the  middle  is 
a horizontal  diaphragm  capable  of  withstanding  the  hydrostatic 
pressure  necessary  for  rapid  filtration.  The  lower  section  of  the 
cylinder  is  filled  with  the  filtering  material,  which  consists  of  two 
parts  of  coke  and  three  parts  of  sand.  The  upper  part  of  the  cyl- 
inder is  used  for  washing  the  filtering  material,  which  is  transferred 
to  it  at  regular  intervals  in  a state  of  violent  agitation  by  hydraulic 
currents,  and  the  impurities  flow  away  through  pipes  situated  near 
the  surface.  The  water  is  admitted  through  pipes  to  the  upper 
part  of  the  lower  section  of  the  cylinder,  and  it  is  drawn  out 
through  perforated  cups  which  admit  the  water  but  exclude  the 
sand.  The  efficiency  of  this  system  depends  more  upon  the  suc- 
cessful precipitation  and  entanglement  of  germ  life  by  the  coagu- 
lent  than  upon  the  merits  of  the  filter.  Aerating  systems  are  also 
attached  to  large  plants,  and  are  said  to  give  excellent  results.  The 
Hyatt  system  is  not  only  one  of  the  most  perfect  for  central  puri- 
fication, but  it  is  also  successfully  used  for  private  supplies. 


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